1. Field of the Invention
The present invention relates to a hydrocarbon analyzer and a method of analyzing hydrocarbons, in particular to a hydrocarbon analyzer and a method of analyzing hydrocarbons in which an exhaust gas from vehicles and other sample gases are transferred to a column with a carrier gas and methane or nonmethane hydrocarbons separated in said column are measured.
2. Description of the Prior Art
Analyzers, in which components of a sample gas, such as an exhaust gas from vehicles, are separated by a column and methane and nonmethane hydrocarbons are measured, as shown in, for example, FIGS. 10 to 13, have been known. Referring to FIGS. 10 to 13, reference numeral 1 designates a 10-way change-over valve with which a carrier gas line 2, a sample gas line 3, a sample gas-discharging line 4, a measuring pipe 5, a first adsorption column 6 and a second adsorption column 7 are connected, respectively. Reference numeral 8 designates a branched line branched from said carrier gas line 2 to be connected with said 10-way change-over valve 1, reference numeral 9a designating a by-pass line branched from the downstream side of said second column 7 to be connected with the 10-way change-over valve 1, reference numeral 10 designating a hydrogen flame ionization detector connected with the downstream side of the second column 7, and reference numeral 11 designating a resistance connected with said branched line 8 set so as to be almost equal to the total of a resistance of said first column 6 and a resistance of the second column 7.
By means of the 10-way change-over valve 1, the carrier gas line 2 can be connected with (and separated from) the upstream side of measuring pipe and the downstream side of first column 6, said sample gas line 3 with sample gas-discharging line 4 and the upstream side of the measuring pipe 5, the downstream side of the measuring pipe 5 with the upstream side of the first column 6 and the sample gas-discharging line 4, by-pass line 9a with the branched line 8 and the upstream side of the first column 6, and the upstream side of the second column 7 with the downstream side of the first column 6 and the branched line 8.
In the above-described analyzer, when the 10-way change-over valve 1 is changed over as shown by a full line, a schematic diagram is as shown in FIG. 11. The measuring pipe 5, the first column 6, the second column 7 and said hydrogen flame ionization detector 10 are connected with the carrier gas line 2 in the order described while the branched line 8 is connected with the by-pass line 9a. When the 10-way change-over valve 1 is changed over as shown by a broken line, a schematic diagram is as shown in FIG. 12. The measuring pipe 5 is separated from the carrier gas line 2, the sample gas line 3 being connected with measuring pipe 5, and the downstream side of the measuring pipe 5 being connected with the sample gas-discharging line 4, so that an appointed quantity of sample gas introduced into the sample gas line 3 may be stored in the measuring pipe 5 while the carrier gas line 2 is connected with the downstream side of the first column 6, the by-pass line 9a being connected with the upstream side of the first column 6, and the branched line 8 being connected with the upstream side of the second column 7. In order to measure methane and nonmethane hydrocarbons, a line shown in FIG. 11 is constructed under the condition that the 10-way change-over valve 1 is changed over as shown by the full line so that the sample gas stored in the measuring pipe 5 may flow from the first column 6 to the second column 7 by a carrier gas in the carrier gas line 2. The respective components of the sample gas are repeatedly adsorbed-desorbed during the passage of the sample gas through the first column 6, but differences are produced in time from a point of time when they are adsorbed by the first column 6 due to differences in molecular weight of the respective components and the like, so that oxygen and methane are desorbed faster and eluted from the first column 6 faster to be transferred to the second column 7. On the other hand, elution times of nonmethane hydrocarbons are comparatively long, so that they are adsorbed by the first column 6 to be left in the first column 6.
Oxygen and methane transferred to the second column 7 are desorbed in the order described to be eluted from the second column 7 with an interval and then transferred to the hydrogen flame ionization detector 10, so that the hydrogen flame ionization detector 10 detects oxygen and methane in turn to put detected signals in a recorder (not shown). O.sub.2 (oxygen) and CH.sub.4 (methane) appear on a chromatogram, as shown in FIG. 13, on the basis of the respective signals put in, so that oxygen and methane are separately measured on the basis of peaks appearing on the chromatogram.
After measuring oxygen and methane in the above-described manner, the 10-way change-over valve 1 is changed over as shown by the broken line to construct a line shown in FIG. 12. In this line, the carrier gas in the carrier gas line 2 is backflushed through the first column 6 from the downstream side to the upstream side to elute the nonmethane hydrocarbons from the first column 6, followed by being transferred to the hydrogen flame ionization detector 10, thus expressing the non-CH.sub.4 (nonmethane hydrocarbons) with an interval after CH.sub.4, as shown in a chromatogram in FIG. 13, so that the nonmethane hydrocarbons are measured on the basis of a peak of the non-CH.sub.4.
Consequently, in the conventional analyzer, at first oxygen and methane are measured with an interval, as shown in FIG. 3, and then the carrier gas is backflushed from the downstream side to the upstream side to transfer the nonmethane hydrocarbons within the first column to the hydrogen flame ionization detector 10 to be measured, so that a time required for measuring the respective components is prolonged. Accordingly, in the case where concentrations of the components are changed within a relatively short time, as in an exhaust gas from vehicles, problems occur in that, for example, it becomes difficult to correspond to the change of the components in concentration and thus a reliability of measurement is lowered. In addition, since methane and nonmethane hydrocarbons are detected in turn by means of one hydrogen flame ionization detector 10, a sensitivity of detection is dependent upon high concentrations of methane or the nonmethane hydrocarbons, so that a problem occurs also in that lower component concentration results in reduced accuracy of measurement.
On the other hand, in view of the fact that the nonmethane hydrocarbons are mainly measured, the first column 6 shown in FIG. 10 has a construction as shown in FIG. 14 in order to elute the high-boiling-point hydrocarbons longer in elution time faster and thus reduce their tailing when it is backflushed with the carrier gas. Referring to FIG. 14, reference numeral 13 designates a first column pipe. A front member 14 made from a carrier made of materials hardly adsorbing the components of sample gas and coated with silicone liquids having a reduced polarity is arranged on the upstream side of said first column pipe 13 and a rear member 15 made from adsorbers, or said adsorbers coated with liquids, is arranged on the downstream side of the first column pipe so that the rear member 15 made from the adsorbers may be larger than the said front member 14 in component-adsorbing power.
The front member 14 adsorbs the high-boiling-point hydrocarbons and desorbs low-boiling-point hydrocarbons. The desorbed low-boiling-point hydrocarbons are transferred to the rear member 15. The rear member 15 adsorbs the low-boiling-point hydrocarbons other than methane transferred from the front member 14 to elute methane faster, whereby methane is transferred to the second column 7. Accordingly, as above described, referring to FIG. 12, when the first column 6 is backflushed with the carrier gas, the high-boiling-point hydrocarbons adsorbed by the front member 14 having a comparatively small adsorbing power are easily eluted and introduced into the hydrogen flame ionization detector 10 as they are. In addition, the low-boiling-point hydrocarbons adsorbed by the rear member 15 are also comparatively easily eluted and transferred to the hydrogen flame ionization detector 10 within a short time, so that the nonmethane hydrocarbons within the first column 6 can be measured as one peak with reducing their tailing.
Components, such as alcohols, having an OH-group and thus high in polarity, are rarely contained in the exhaust gas from vehicles and other sample gases; and thus it has been possible to measure the nonmethane hydrocarbons contained in them with reducing their tailing by means of the conventional nonmethane hydrocarbon analyzer. However, recently fuels also containing components, such as alcohols, having an OH-group and thus high in polarity, have been used. Accordingly, if the sample gas containing the components, such as alcohols, having an OH-group and thus high in polarity, is introduced into the first column 6, as shown in FIG. 14, oxygen and methane desorbed and are eluted from the first column 6 faster during the passage of the sample gas through the first column 6 to be transferred to the second column 7.
However, the front member 14 of the first column 6 adsorbs the components having an OH-group in addition to the high-boiling-point hydrocarbons, so that the components having an OH-group are strongly adsorbed by the front member 14 to tail during the backflushing. As described above, referring to FIG. 12, when the carrier gas is backflushed from the downstream side to the upstream side of the first column 6; that is, the carrier gas is backflushed from the side of the rear member 15 to the front member 14 of the column 6, as seen in FIG. 14, the components, such as alcohols, having an OH-group and thus high in polarity, are eluted with difficulty from the front member 14; and thus it takes a longer time to pass through the front member 14, so that it takes a remarkably long time to measure the respective nonmethane hydrocarbon components. Moreover, a problem occurs in that the tailing occurs to make the measurement impossible. In short, it is impossible to measure the whole quantity of nonmethane hydrocarbons adsorbed by the column at high speed with reducing the tailing.